Simplify the following expression: $n = \dfrac{1}{5z} - \dfrac{9}{2z}$
In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $5z$ and $2z$ $\lcm(5z, 2z) = 10z$ $ n = \dfrac{2}{2} \cdot \dfrac{1}{5z} - \dfrac{5}{5} \cdot \dfrac{9}{2z} $ $n = \dfrac{2}{10z} - \dfrac{45}{10z}$ $n = \dfrac{2 -45}{10z}$ $n = \dfrac{-43}{10z}$